Extensometer



GI H. BENEDICT.

EXTENSOMETER. APPLICATION FILED OCT. 8. I919.

Patented. Nov. 15, 1921.

G. H, BENEDICT EXTENSOMETER.

-APPLICATION FILED OCT. 8. 1919.

Patented Nov. 15, 1921.

2 SHEETS-SHEET 2.

I721?) 677/ 2 507 w MM EXTENSOMETEE.

Specification of Letters Patent.

Patented Nov. 15, 1921..

Application filed Gctober 8, 1919. Serial 1T0. 329,351.

(FILEDUNDER THE ACT OF MARCH 3, 1883, 22 STAT. L, 825.)

To all whom it may concern:

Be it known that l, Gnonen l-l. Bnnnnrc'r, a citizen of the United States, and a resident of Schenectady, county of Schenectady, State of New York, have invented an improvement in Extenso netersy otwhich the following is a specification.

The invention described herein maybe used by the Government, or any of its otficers or employees in prosecution of work for the Government, or by any other person in the United States without payment of any royalty thereon.

My inventionrelates to an extensometer device applicable for use in connection with the usual physical tests applied to materials employed in commercial manufacture.

Its objects are to provide an instrument which is sutliciently delicate to read accurately to very small dimensions but which is also sufiiciently substantial to possess wear resisting qualities so that the mechanism cannot be easily deranged or, put out of working order.

A further object of this invention is to provide a precision measuring instrument of this type which may be readily applied to and removed from'the test specimen.

.lnthe description which follows reference will be made to the accompanying drawings in which like reference numerals indicate corresponding parts throughout the several views.

' Figure 1 is an elevation of my invention with the parts in normal position and having the cover plate removed.

Fig. 2 is an elevation with the parts in extended position and having the cover plate removed.

Fig.3 is an end view showing the cover plate in place. I

Fig. l is a partial sectional view of a tool for making data mark i The main working partsoi my invention are inclosed in the shallow boxlike casing 10 the top of which is formed with an interrupted and slightly depressed ledge 12 having threaded openings for the reception of machine screws-which retain the detachable cover plate in place. The amount of depression of the ledge 12 is such that the cover plate is flush with the top of the worklng parts so as to retain them in operative relation and so that outside of the cover plate is preferably flush with the top of the sides of casing 10.

ltiveted to the back plate of casing 10 are the duplicate, bearing members A having socket bearings which provide closely fitting journals for the cylindrical shaped lower ends of registering bar supporting arms 5 and the cylindrical shaped upper ends of working bar supporting arms 4:. The casing is preferably made of bronze and the bearing members 14 and arms 4, 5 of steel so that the rounded ends of arms l, 5 and the corresponding bearing surfaces may be hardened it desired in order to furnish wear resistant surfaces but this is not necessary since the bearing surfaces provided are ample and if any wear should occur it will be uniform throughout the bearings and will not therefore impair the accuracy of the mechanism.

The lower cylindrical shaped ends of arms 4 are journaled in bearing sockets at opposite ends of working bar 1. All of the bearing sockets of this device are formed so that the material forming the socket extends a considerable distance past the semicircle at any section. Therefore when the cylindrical ends of the supporting arms are inserted into the sockets and the cover plate is secured in place flush against the top of the socket bearings, the supporting arms l, 5 are securely held in operative position within the socket bearings 14k.

in view of this connection of the working bar 1 with registering bar 8 through arms l, socket bearings i l and arms 5 these bars are always substantially parallel.

- Projecting from the upper sideoit bar 1, is a lug 1'7 and projecting from bar 3 is a lug 18. A pivot pin 15 projects upward from the back plate of casing 10 and provides a pivot for multiplying lever 2. The multiplying lever 2 is or such thickness at its hub portion to it snugly under the cover plate so that it is retained in operative position thereby. The pivot 15 is located near lug 1! so that the movement communicated to the lever by his" 17 is transmitted to lug 18 in multiplied term which is preferably some simple multiple as one to ten.

Secured to the lower side of working bar 1 and preferably integral therewith is a hardened point 9 called the movable point and secured to the lower side of the casin D is the hardened point 11 called the fixed point, the function or which points will be hereinafter described. When the working bar 1 is operative position the point 9 projects through an elongated slot formed in the side wall of casing 10. j 9 and 11 are such length as to extend the same distance from the side wall of the casing.

The registering bar 2-3 has at one end an upright split ex ension 19 which is threaded for engagement with adjusting screw 7. The extension 19 projects through and is movable in an elongated opening in the upper side of casing 10. The screw 7 is adjusted so as to just contact with the end of operating stem 21 of a micrometer indicator having a graduated dial and a pointer which is capable or"- making a complete revolution for a small longitudinal movement of the stem, and thus give an easily readable measurement of a very small quantity. The specific :torm of indicator forms no part of my invention it being understood that any suitable type of commercial indicator can be used without departing from the spirit or scope of my invention. The indicator shown on the drawing is secured to the upper side of casing 10 by means of screws 20.

A holding block extends below the casing and is secured to the back plate of easing 10 in any suitable manner as by means of screws 22. The holding block having the 4 C a Q short portion A and iong portion 20 is L- shaped. The portion 2 is formed with a central hole which is threaded for screw 25. The long portion 28 is slotted and the two 'parts of this slotted portion are slidably engaged by a V-block clamp attachment which comprises the wide V-clamp, and a wide rear extension 26. The rear extension is inserted while in endwise position through the slotted portion and then the V- clamp attachment is turned to upright position. Since the portions 6 and 26 of the clamp attachment are wider than the slot, the clamp attachment is slidably supported. The screw 25 extends upward through a hole in extension 26 and is retained therein 7 against rotation by means oi": pin 27. A nut 28 engages the. threads of screw 25 and abuts agianst one side of portion 2a. A spring 29 surrounding screw 25, is compressed between stationary member 24 and extension 26 and thus tends to force the V-clamp block upward.

\Vherea large number of test specimens of a specified form are used and the data marks are originally a given distance apart, a marking tool similar to the type shown in Fig. 4 may be advantageously used, in which the marking points 30 and 31 are the given distance apart, and the interior of the tool of the general contour of the body of The points the test specimen, such tool also having the flattened head32 on which impact is made in order that the points 30 and 31 may make proper indentations or data marks in the test specimens.

In operation the data marks are first made on the test specimen, preferably by the device shown in Fig. 4-, and the test piece is then placed in the testing machine. The extensometer is then placed upon the test piece, the two points 9 and 11 being placed in the data marks, and the nut 28 adjusted so that the extensometer is held in place by the V-block clamp which is acted upon by spring 29 with sufiicient force to keep the points 9 and 11 firmly seated. The screw 7 is then adjusted so that when a slight initial stress is placed on the test piece a minute elongation will be recorded. The screw 7 is then delicately adjusted until the indicator reading is brought back to zero.

As the stress is applied to the test piece the movable point 9 moves as the metal elongates thereby causing the point 9 and working bar 1, to move with the elongations of the metal. The multiplying lever 2, transmits this movement to the registering bar 3 in an increased ratio of preferably one to ten. This increased movement of recording bar 3 is registered in multiplied form by the indicator 8, by means of screw 7 which moves with bar 3 contacting with the stem 21 of the indicating instrument. injury to the mechanism by the shock that occurs when the test piece breaks the extensometer is usually disconnected after the elastic limit of the material or" the test piece has been reached.

This instrument gives a definite, and accurate indication of the elastic limit of the material either by noting successive readings given by equal load increments in order to find the point where elongation ceases to be proportional to the tensile stress or by returning to the initial load after each additionalstress until permanent set is indicated.

Having described my invention, what I claim as new and desire to secure by Letters Patent, is I 1. An extensometer comprising a casing having a point fixed with reference thereto, a movable working bar mounted in said casing and having a second point secured there- To prevent" intermediate socket bearings secured to said casing, a registering bar having socket bearings, supporting arms for said registering bar mounted in said socket bearings, a Working bar, a pivoted lever for communicating motion from said Working bar to said registering bar and a cover plate for retaining said supporting arm and pivoted lever in operative position.

4. An extensometer including a casing having a point fixed with reference thereto, a Working bar having the movablepoint secured thereto, a registering bar, means for communicating motion from said Working bar to said registering bar, an indicator and means adjustable in said registering bar, for actuating said indicator.

5. In an extensometer, a casing containing a movable Working bar, a registering bar, a pivoted lever, supporting arms for said bars, and a removable cover plate for said casing for retaining said parts in operative position.

GEORGE H. BENEDICT. 

